1. Field of Invention
This invention relates to a method and composition for inhibiting the corrosion of sodium and calcium chlorides and, in particular, to a method and composition ideally suited for treatment of rock salt used for deicing roads and highways.
2. Background of the Invention
Sodium and calcium chloride are widely used industrial chemicals. Perhaps the most commonly observed application of sodium and calcium chlorides is the use of these salts as a road cover in freezing climates, where their high solubility depresses the freezing point of water, thereby melting ice and snow on the surfaces to which it is applied. Other applications of significant volume are the use of calcium chloride as a curing accelerator in concrete, as an additive in drilling muds to control density and clay flocculation, as a drainage aid in paper mills, as a high density liquid used as ballast in tractor tires, and as a desiccant in refrigeration plants.
A common problem experienced in the various applications of sodium and calcium chloride is that the salts promote corrosive attack on metal surfaces. The corrosiveness of sodium and calcium chloride brines is particularly troublesome in the road cover applications where the brine which is splashed on the undersurfaces of cars can cause rapid corrosion and deterioration of the under panels and rocker panels of a car. Since modern car manufacturing techniques have almost universally adopted unitized construction for weight and manufacturing efficiencies, any corrosive attack of brines on the undersurfaces of automobiles is particularly troublesome as the deterioration of such surfaces by corrosion is often not economically repairable. Furthermore, the salts added to roads adversely affects roadside vegetation and has been observed to have killed roadside trees. These salts are frequently transported as saturated brine solutions in pipeline, and their corrosiveness to steel presents a significant problem to such handling.
The use of calcium chloride brines in other applications such as concrete curing accelerators or as additives to drilling muds also creates serious corrosion problems. Most construction concrete is reinforced with steel bars which are embedded in the concrete and the presence of calcium chloride in the concrete accelerates corrosive attack of the reinforcing steel. The calcium chloride in drilling muds causes an accelerated corrosion of well tubing and equipment used in oil drilling applications. The use of calcium chloride as a drainage aid in the paper industry has been limited by the corrosive nature of its solutions.
The problem of accelerated corrosion by sodium and calcium chloride brines is thus a problem which has not, heretofore, been adequately addressed by the prior art. Some solutions to the problem have included the substitution of other salts such as calcium or magnesium acetates or chromates for the road cover applications. These substitutions are not satisfactory because of a prohibitively high cost and because of potentially adverse effects on the environment.
Ideally, any corrosion inhibitor used with sodium and calcium chlorides should be effective at extremely low concentrations to minimize environmental problems and should be colorless to avoid staining or discoloring of metal surfaces, wearing apparel and the like which come in contact with brine solutions of sodium or calcium chloride. The inhibitor should be effective over a very wide range of concentrations, particularly when applied for inhibiting corrosion of brines used in road covers since the brines which are formed by melting of ice and snow in the presence of sodium and calcium chloride can be expected to have an extremely wide range of concentration of the sodium and calcium chloride. The inhibitor should also be soluble over the wide range of concentrations anticipated in its application.